Phospholipids play critical roles in hormone sensitive adenylate cyclase systems. Solubilized preparations of myocardial adenylate cyclase are unresponsive to stimulation by glucagon and catecholamines. Responsiveness to glucagon can be restored by the addition of phosphatidylserine and responsiveness to catecholamines by monophosphatidylinositol. Glucagon specifically increased the synthesis of phosphatidylserine in slices of heart muscle. We have also demonstrated a dissociable glucagon binding site and separated the glucagon binding site from the catalytic site by Bio-Gel and Sephadex chromatography. We will study the effect of catecholamines on the synthesis of monophosphatidylinositol and determine the relationship of cyclic AMP to phospholipid synthesis in heart muscle. We will also determine the role of the fatty acid side chains in the phospholipid effects on restoratin of hormone responsiveness. Particular attention will be focused on arachidonic acid and prostaglandins and attempts will be made to localize the site of prostaglandin action using 3H-prostaglandins. The results of the phospholipid experiments will be correlated with electronmicroscopic observation of sarcolemmal gap junctions the potential area of the membrane containing the hormone receptor. There will be additional autoradiographic studies of gap junctions using radiolabeled phospholipid precursors. We have isolated a peptide-inhibitor of adenylate cyclase from rat liver. The unique peptide has been purified 50,000-fold and will be sequenced and synthesized. It should enable us to determine which physiologic processes in the heart are cyclic AMP-mediated and those which are not. The peptide may have extraordinary diagnostic and therapeutic implications. Other studies will include hormone interactions with guanylate cyclase and the role of cyclic GMP in hormone action. We have found that cyclic GMP levels are decreased in livers of diabetic rats and rapidly restored by insulin administration.